Add option to run linter with tests

[mikepurvis]

For example:

roslint_python(src/mypkg/foo.py AS_TEST lint_python)

We would create the roslint and roslint_mypkg targets as usual, but also create a run_tests_mypkg_lint_python target, depended upon by run_tests. The idea would be that you could optionally have the linter check run as part of the CI's run_tests build.

On the implementation side, we should be able to call catkin_run_tests_target to wire it up, though you need to provide xunit xml output for that; that aspect of this intersects with #9. (And there may need to be transformation stage in there, to coerce the line-by-line output into the requisite XML.)

[jack-oquin]

+1 Good idea.